JPH11265956A - Cavity package - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a low-priced cavity package of high reliability. SOLUTION: This cavity package is hardened by injecting a low adhesive coating material 11 into a cavity region 13 in such a manner that the upper surface of an IC die 17 is not coated. The boundary between the main body of a package 14 and a metal contact 15 is sealed by the above-mentioned coating, and the intrusion of a liquid into the cavity region is prevented even when there is a gap on the boundary. Also, a package cover 19 and the package main body 14 are formed using a thermoplastic material, and the cover and the package main body can be welded easily by giving an ultrasonic pulse to the junction part of the cover and the package main body only.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an integrated circuit (IC).
The field of package design and manufacturing. The embodiments described herein relate specifically to the packaging of radio frequency (RF) and microwave ICs.

[0002]

2. Description of the Related Art When used for microwave and high frequency ICs, an IC package having a cavity therein is more preferable than a tightly sealed package.
The inherent permittivity and loss factor of the polymer encapsulant have a parasitic effect on the propagation of high frequency signals. This occurs when a molding polymer is used as a sealing material for microwave or high frequency ICs and is in direct contact with the active area on the top surface of the IC die. Encapsulation (enca
Psulation) is a standard, well-known method of creating low cost packages of this type of IC. The well-known cavities made of ceramic, metal or glass
Packages have been expensive both in the materials used to make the packages and in the methods required. Cavity packages made using polymers and made using molding techniques similar to those used in the encapsulation process are well known and are more cost effective than standard sealed packages. It is advantageous. One such package is February 2, 1994.
Pending U.S. patent application Ser.
No. 316, "Integrated Circuit Package With Improv
ed High Frequency Performance ”.

One problem with cavity molded plastic packages is that liquid plastic may penetrate the cavity due to the separation of the interface between the inserted molded metal conductor element and the molded plastic. This problem is greater for cavity packages where the conductive metal elements are flush with the bottom of the package. Placing the conductor path on the bottom surface in this way improves high frequency performance, but mechanically weakens the interface between the molded plastic and the metal. Gaps may be created at this interface if large stresses are caused by different coefficients of thermal expansion or other factors. The adhesion of the polymer to the metal lead frame is at its best when mechanical and chemical bonds to the metal are formed, but this bond can vary consistently in a manufacturing environment. Depends on factors.

[0004] Another problem with cavity plastic packages is the attachment of the lid to the package.
There are three known methods for attaching a lid to a package. An adhesive polymer (typically an epoxy "B" stage) previously molded as a seal ring may be affixed to the lid by a lid vendor. When placed on a plastic body, the appropriate location on the lid is heated to cause a catalytic reaction of the epoxy. Next, the completed package is cured. Alternatively, an alloy of the eutectic composition that acts as a preformed seal ring may be affixed to the lid by a lid vendor. This alloy is heated by pressure contact with the package body,
Form a braised joint to seal the package. A glass preformed seal ring can be used in the same way as a eutectic preformed seal ring, but this seal relies on the interaction of the oxide with the metal surface.

[0005] Each of the known methods of attaching a lid to a plastic cavity package has problems. When using sticky polymers, sealing integrity may be compromised by processing conditions, misalignment, lot-to-lot variation of material, surface conditions and compatibility of the material at the sealing interface. The lid must be transported and secured until it is ready for assembly. Eutectic alloys and glass encapsulation are too expensive for many applications, and the temperatures required for adequate quality encapsulation are too high for low cost packaging materials such as molded plastics and die attach. Also, such sealing requires expensive process control equipment, including atmosphere control, and strict process control.

[0006]

Accordingly, there is a need for a method and apparatus for sealing the interface between a molded package body and a metal contact to prevent liquid from entering the cavity area. Further, there is a need for a more appropriate method for attaching a package lid to a cavity package.

[0007]

SUMMARY OF THE INVENTION The present invention, in a first preferred embodiment, is a performance enhancement to a plastic cavity package wherein a low viscosity coating similar to the cavity area does not cover the top surface of the IC die. In the cavity region. This similar coating seals the boundary between the molded package body and the metal contacts,
The cavity is protected from liquid intrusion into the cavity area even if there is a gap at the boundary of the metal / mold composite.

In a second embodiment, a plastic
The lid and package body of the cavity package are both made of a thermoplastic material, which can be fused using a pulse of ultrasonic energy directed only to the junction between the lid and the package body.

A preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings and the following description.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In a first preferred embodiment of the present invention shown in FIG. 1, a low viscosity coating 11, similar to the bottom of a cavity, is injected into a cavity region 13 of a cavity package 10. Coating 1 around the die using a small diameter syringe operated by a robotic device
1 can be injected. The coating 11 seals the boundary between the molded package body 14 and the metal contacts 15 so that liquid does not penetrate the cavity region 13 even if there is a gap between the metal and the molded polymer. The package is completed by the lid 19.

In this embodiment, the top surface of IC die 17 is intentionally left uncoated. The low viscosity polymer forms a coating similar to the bottom surface of cavity 13.
This coating is cured with ultraviolet light (“UV”) and ultimately only exists around the die 17 and does not contact the active area on the top surface of the IC die 17. Alternatively, a heat-curable, low-viscosity polymer can be used. If there is a coating on the top surface of the IC die 17, the purpose of the cavity package will not be achieved because the coating will degrade the performance of the IC.

In a second embodiment of the present invention, both the lid and the body of the cavity package are made of a thermoplastic material. Such thermoplastic materials can be fused using a pulse of ultrasonic energy that is directed and affects only the interface between the lid and the package body. This is a common bonding process for thermoplastics in some manufacturing plants, but has not previously been used for packaging microwave and high frequency ICs.

FIG. 2 is a cross section of a microwave and high frequency IC cavity package with an ultrasonically fused lid. The IC package 50 includes a package body 51 having a metal lead frame 53 embedded therein and a wire bond 52 mounted on the lead frame.
And a semiconductor IC die 55 joined together. Air cavities 57 can improve package performance in microwave and high frequency applications. The lid 59 is
It is made of the same thermoplastic material as the main body 51, and is ultrasonically fused 61
Is fused to the main body 51 by ultrasonic means.

Since the lid and the body are made of the same material, they become a single-phase material of homogeneous composition at the location of the ultrasonic fusion. Other known processes for joining the lid and body require a different layer of material at the joint, and this layer of material has low surface wettability, erosion, and intermetallic growth.
Interfacial interactions such as ic growth, mismatch in the rate of expansion after assembly ("TCE"), and the like, can reduce the integrity of the package.

This is a manufacturing process that is extremely easy to reproduce because the lot-to-lot and process-to-process variations and surface conditions are not important factors for ultrasonic welding. Key process parameters are ultrasound frequency, amplitude, and dwell time. Ultrasonic welding can also be self-aligned. Care must be taken in the process parameters selected to avoid damaging the IC die in the package body, but ultrasonic energy has already been used to form a wire bond between the IC die and the metal lead frame. Note that

[0016] Ultrasonic fusion has a short down time of the ultrasonic energy and does not require oven adjustment time, fixture preparation time, and temperature cure profile time,
Can be used for mass automated assembly. Also, the cost of the apparatus is sufficiently low since no preformed seal rings are required.

[Embodiments] Examples of embodiments of the present invention are shown below.

[Embodiment 1] Cavity of integrated circuit
A method of sealing a lid to a package (50), comprising forming a lid (59) and a package body (51) from a thermoplastic material, and fusing the lid to the package body using ultrasonic energy. And a step.

Embodiment 2 A cavity package (10) including a step of injecting and curing a low-viscosity coating (1) in a cavity of the package so as not to cover the upper surface of the integrated circuit (17) in the package. A) preventing the liquid from entering the cavity (13).

[Embodiment 3] A package body (14) having a cavity (13) having a side wall and a floor surface, and a metal lead embedded in the package body with its upper surface exposed to the floor surface of the cavity. A frame, a top surface of the metal lead frame, an integrated circuit coupled thereto, and a top surface of the cavity disposed so as not to cover the top surface of the integrated circuit, forming a coating analogous to the floor surface of the cavity; Low viscosity liquid polymer that cures in place (11)
And a lid (19) attached to a side wall of the package body.
Wherein the space between the bottom surface of the lid and the liquid polymer forms a cavity.

[Embodiment 4] A package body (51) provided with a cavity (57) having a side wall and a floor surface,
A metal lead frame (53) embedded in the package body with the upper surface exposed to the floor of the cavity;
An integrated circuit (55) disposed on and coupled to the top surface of the metal lead frame, and a lid (19) attached to a side wall of the package body, between the bottom surface of the lid and the floor of the package body. The cavity package forms a cavity, and the lid is attached to the package body by an ultrasonic sound source.

[Embodiment 5] A package body (51) having a cavity (57) having a side wall and a floor surface, and a substrate (53) embedded in the package body with an upper surface exposed to the floor surface of the cavity. And an integrated circuit (55) disposed on and coupled to the top surface of the substrate, and a lid (59) attached to the side wall of the package body, the space between the bottom surface of the lid and the floor of the body. Forming a cavity, wherein the lid is attached to the main body by an ultrasonic sound source.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a cavity package showing a first preferred embodiment of the present invention.

FIG. 2 is a cross-sectional view of a cavity package showing a second embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Cavity package 11 Coating 13 Cavity 14 Package main body 15 Metal contact 17 Die 19 Lid 50 Package 51 Package main body 52 Wire bond 53 Metal lead frame 55 Die 57 Air cavity 59 Lid

Claims (1)

[Claims] 1. A package body having a cavity having a side wall and a floor surface, a metal lead frame embedded in the package body with an upper surface exposed to the floor surface of the cavity, and an upper surface of the metal lead frame. And a low viscosity liquid that is placed on the floor of the cavity so as not to cover the top surface of the integrated circuit, forms a coating similar to the floor of the cavity, and cures in place. A cavity package comprising: a polymer; and a lid attached to a side wall of the package body, wherein a space between a bottom surface of the lid and the liquid polymer forms a cavity.